Patterns of phrenic motor output evoked by chemical stimulation of neuronslocated in the pre-Botzinger complex in vivo

The pre-Botzinger complex (pre-BotC) has been proposed to be essential for respiratory rhythm generation from work in vitro. Much less, however, is kn own about its role in the generation and modulation of respiratory rhythm i n vivo. Therefore we examined whether chemical stimulation of the in vivo p re-BotC manifests respiratory modulation consistent with a respiratory rhyt hm generator. In chloralose- or chloralose/urethan-anesthetized, vagotomize d cats, we recorded phrenic nerve discharge and arterial blood pressure in response to chemical stimulation of neurons located in the pre-BotC with DL -homocysteic acid (DLH; 10 mM; 21 nl). In 115 of the 122 sites examined in the pre-BotC, unilateral microinjection of DLH produced an increase in phre nic nerve discharge that was characterized by one of the following changes in cycle timing and pattern: 1) a rapid series of high-amplitude, rapid rat e of rise, short-duration bursts, 2) tonic excitation (with or without resp iratory oscillations), 3) an integration of the first two types of response s (i.e., tonic excitation with high-amplitude, short-duration bursts superi mposed), or 4) augmented bursts in the phrenic neurogram (i.e., eupneic bre ath ending with a high-amplitude, short-duration burst). In 107 of these si tes, the phonic neurogram response was accompanied by an increase or decrea se (greater than or equal to 10 mmHg) in arterial blood pressure. Thus incr eases in respiratory burst frequency and production of tonic discharge of i nspiratory output, both of which have been seen in vitro, as well as modula tion of burst pattern can be produced by local perturbations of excitatory amino acid neurotransmission in the preBotC in vivo. These findings are con sistent with the proposed role of this region as the locus for respiratory rhythm generation.